Boy, do I know how you feel...! Your profile doesn't say how many dives you have logged, though, so I'm not completely clear where you coming from...?
Not sure where this came from: "...how do i know somebody is not gong to hit me over the head for my stuff or worse." Maybe you're talking about trips, or shore dives...?
If you're talking about trips, you go with groups - best way to deal with this fear, as the worst I've ever had from an assigned roomie was when he borrowed my nail clippers and hair brush without asking, then stole my last six pack. He was also too green to be on that boat, so I just privately refused to buddy with him; I got a good one, and someone who owed the leader a favor suffered. {Yes, he was from Arkansas.}
If you're talking about meeting for shore diving, I have no experience, but I'd say about the same - organize groups.
Now my From-Hell experiences have been when I traveled alone to dive, Florida Keys, Catlaina Is CA, etc on day boats. Being a singular, I generally get the leftover boat-pick no one else wanted, and it's been a hoot. 2 times in one week, with different operators, I dived on the S.Grove, only to have each of my assinged buddies show me 500 psi left at 80 feet. Damn! What if I needed air? Dive aborted early so we can get back on my 1500 psi. No refunds. And I have other stories.
If you can find a good, compatible buddy and arrange to go together, that's great, but I can't. People here don't travel much, much less travel & dive, so most trips I go alone.
I hope for the best, never dive without a pony, and if the assigned buddy turns out to be an air hog, I ask them to stay above me a few feet at all times - to slow them down a bit.
